This invention relates to a dart-operated big bore by-pass tool for use in a drill string.
Some drilling operators require a circulation tool with a large through-bore to allow for retrieval of MWD probes and nuclear sources, but this can cause difficulties when there is a requirement, which arises from time to time during drilling, to by-pass the flow of fluids in the drillstring by directing the fluids through one or more by-pass port.
It is already known from U.S. Pat. Nos. 4,889,199 and 5,499,687 to provide a by-pass tool which has an axially displaceable sleeve (which is spring-loaded to an inactive position in which it blocks communication between the interior of a drillstring and one or more by-pass port) so as to allow normal flow of fluids lengthwise of the drillstring. However, a valve seat is provided which is arranged to receive a deformable activation ball (launched from the surface and travelling down the drillstring), and which then creates a pressure build-up resulting in the valve seat and the sleeve moving downwardly so as to uncover the by-pass port and allow by-pass flow of fluids. The tool therefore can be ball-activated so as to take-up an active by-pass mode.
When it is required to re-set the tool, a smaller hard ball is launched from the surface and which forces the larger and deformable activation ball (used to activate the tool) through the valve seat so that the sleeve then returns to its original position (covering the by-pass port).